1. Field of the Invention
This invention concerns a reciprocating piston pump for the pulsation-free delivery of a liquid with the use of at least two cylinders connected in parallel on their discharge side, of which one in each instance sucks and the other delivers, in which the pistons working in said cylinders are controlled by cam means, and in which each piston, for the purpose of compensating for the compressibility of the liquid, is caused to perform a precompression stroke before each delivery stroke.
Reciprocating piston pumps of the aforesaid type are employed to supply liquids for use in chromatographic investigations.
2. Description of the Prior Art
In a known reciprocating piston pump as disclosed in the German Specification No. 2,446,805 laid out for public inspection the length of the precompression stroke is adjusted to the compressibility of the liquid to be pumped in order to ensure pulsation-free delivery of the liquid. For the purpose of permitting such an adjustment to be effected, this known reciprocating piston pump is provided with adjusting screws constituting stop means for piston tappets each of which co-operates with a disc cam associated therewith. Said adjusting screws may each be moved into a stopping position in which they are adapted, as a suction stroke is being performed, to intercept the piston tappets before they reach their rearward limit positions so as to preclude any further motion in a rearward direction. Thus, within a predetermined portion of each revolution, the disc cams will come out of contact with their respective piston tappets. The said portion may be considered as being equivalent to a precompression stroke. However, when the operating conditions, i.e. for example the temperature or the viscosity of the liquid or the pressure against which pumping is to be done, and/or the composition of the liquid to be pumped are altered, manual or automatic readjustment will have to be effected. This, in turn, will result in the liquid throughput to be changed.